Why would a guy look away?

I was chatting with one of my guy friends who I have a flirty relationship with. He makes strong eye contact and I have caught him staring at me.

We were talking about times we were in fancy dress. I told him that my favourite fancy dress costume was my French maid outfit. I showed a picture of me wearing said outfit and he gave it a quick glance and then looked away.

It felt a little awkward. Why would he have looked away instantly?

Why would a guy look away?
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